The present invention relates to a dispersion of pyrogenically produced cerium oxide, a method for producing it, and its use.
Dispersing cerium oxide in water is known in the art (EP 0 957 064 A1).
In addition, dispersing pyrogenic cerium oxide in a mixture of water and a base, where the pH of the dispersion is greater than 8, is known from WO 02/40399.
These dispersions can have a solids content up to 40 wt %. High shear mixers can be used to produce the dispersion, with a shear rate of at least 102 sec−1 being used.
The resulting known dispersion can have a service life of more than 7 days at 25° C. and can be used in chemical-mechanical polishing (CMP). To remove grit or particles that exceed a certain size the known dispersion of pyrogenic cerium oxide can be passed through a filter. Very fine filters can also be used in this case, and for which the dispersions should have a low viscosity.
WO 02/40399 does not describe a specific example of an aqueous dispersion of pyrogenic cerium oxide. Furthermore, nothing is said about the average primary particles or the average aggregate size of the cerium oxide. WO 02/40399 also does not give an example in which the filtration of an aqueous dispersion of pyrogenic cerium oxide is carried out.
Experiments by the applicants have shown that an aqueous dispersion of pyrogenic cerium oxide that contains fine particles cannot be filtered. Plugging of the filter develops spontaneously, since a three-dimensional network is formed because of the thixotropic structure of the pyrogenic cerium oxide. Thus, separation of an aqueous dispersion of pyrogenic cerium oxide from coarser particles that are larger than 1 μm is not known in the prior art.